1. Field of the Invention
The present invention relates to a method and apparatus for connecting a first line to a second line. More particularly, this invention relates to a method and apparatus for connecting two or more lines using a remotely operable articulated connector.
2. Description of Related Art
In many industries, it is necessary to connect a first fluid-carrying or electrical line to a second line. In particular, the oil and gas industry regularly utilizes subsea pipelines that must be connected for the gathering and transportation of produced fluids.
There are several methods and devices currently used for connecting lines, and particularly, subsea lines. Methods known in the art include, for example, standard API or ANSI flanges. Alignment and installation of bolting may be performed using a diver or remote equipment. Tools that aid in the assembly of flanges may include alignment guides, modified bolts, or nut retainers. When a connection is made on relatively small pipes and in depths that are readily accessible by divers, the use of flanges has been historically acceptable. On larger pipes and in locations where accessibility becomes a problem for divers and intervention equipment, however, flanges become more difficult to use. Alignment of two flange halves is often time consuming and difficult. Engaging a nut on a bolt may be quite difficult in certain subsea environments. Manipulation and cross threading, which often present significant problems for divers, make many current remote connection techniques impractical.
One technique under development uses pipe handling frames to manipulate a pipe and to align flanges. Tooling must be included to install the sealing gasket and bolting. Examples of this equipment include the Sonsub Brutus system and the Stolt Comex Seaway Matis (Modular Advance Tie In System) System. Although these systems have shown some degree of utility, the equipment associated with this technique may be bulky and relatively difficult to deploy. A typical flanged connection system utilizing subsea rigging may have a length of about 32 feet, a height of about 8 feet, and a weight of about 38 thousand pounds. Mechanisms to install the bolting are usually located well inside the frames, and, therefore, access is often restricted to correct any problems with remote bolt manipulation.
Another technique uses a flanged connection system with a midline ball-and-socket type connector. Although this type of system introduces articulation into the pipe spool, the articulation exhibits significant drawbacks. Articulation at the midline location is often accompanied by X-Y translation at the point of connection. This may be additive to overall misalignment of the connection and may therefore create unwanted stresses near the connection point.
Another technique uses a DFCS (Diverless Flowline Connection System) flexible pipe connection system. This system incorporates a flexible hose. The use of the hose results in reduced stress at the point of connection compared to a rigid steel pipe. However, the hose is limited in use because of manufacturing limitations of size, collapse of the hose from the pressure in deep water, and incompatibility with some aggressive produced fluids that must be transported.
In addition to flange methods, there are other techniques for connecting two lines. One technique uses a clamp-type connector, and the clamp itself provides structural strength. The clamp may include two or more segments that may be drawn together with bolts. Some methods pre-assemble the bolts to avoid subsea assembly. The clamp engages two pipeline hubs, and the sealing is between the two hubs. Another method of engaging the hubs is to use a set of radially oriented collet fingers. The fingers may be rotated into position and provide the structural strength. A set of radially translated dogs may also be used as a locking mechanism. The hubs may be drawn together by the dogs in a manner similar to that of the collet fingers.
Although the above-noted techniques have demonstrated at least a degree of utility in connecting lines, significant room for improvement remains. For instance, such current techniques often require face-to-face contact, without angular misalignment, between lines in order for a successful connection to be made. Such required face-to-face contact means that subsea linear and angular measurements may become critical. For example, if a jumper spool is to be connected to two laterally spaced, upwardly facing pipelines, it is necessary to measure the linear distance between the two upwardly facing pipelines and precisely measure the angular orientations of those two pipelines before the connection may be made. Equipment for making such measurements, especially for making angular measurements, can be extremely costly and complicated, and the measurement process may add significantly to delays, thus further increasing costs in connecting lines. Further, errors in linear measurements may translate into angular errors during connection because angular flexing may be required to compensate for, for instance, a short or long jumper spool. Angular errors may significantly add to stresses occurring at a connection point. Such stresses may degrade a connection and may lead to a short product lifetime.
Other disadvantages may arise in current techniques due to the forces required to make a connection when misalignment is present. The determination of forces required to complete a connection is an integral part of the connector design process. During the installation of the connector, the application of force may be performed by bolting, clamping, collets, and dogs. The connection load is predetermined and is generally difficult to alter. In remote installations, the difficulty increases due to inaccessibility of the equipment. When a line and its final, intended location differ in linear and/or angular dimensions, there is additional unknown load that must be introduced to complete the connections. This is the load required to force the connections into alignment within the tolerance required for sealing. The misalignment may be a combined result of measurement error, pipe spool fabrication, gravitational, and thermal influences--regardless of the source of error, however, the additional load required to connect the misaligned lines increases the probability of an unsatisfactory connection.
Another potential for failure of a connection using current techniques relates to damage to a seal or sealing surface during installation. Because current alignment techniques typically use seal surfaces for alignment, the seal often bumps, for example, a flange of another line during pipeline alignment. Such bumping may scratch or otherwise damage the seal, leading to a faulty connection. This increases the potential for damage to seals and sealing surfaces. When sealing surfaces used for annulus testing are also used for alignment, damage may occur, which may cause the annulus test to fail.
Many current techniques rely upon divers to facilitate the connection process. However, as subsea pipelines are installed deeper, it may become difficult for divers to connect lines. Other techniques may be suitable for divers, but financial concerns may dictate that divers may not be used because of their high cost. Therefore, a technique that may connect lines without divers, but that is inexpensive enough so that divers may be used if wanted would be desirable.
In current deep water connections systems, one of the driving cost factors is the cost of the installation vessel and its ancillary costs. These costs often greatly exceed the cost of the connector. Many activities, including measurement and subsea pipe manipulation to force alignment, may require extensive vessel time. A technique that could reduce installation time would therefore be advantageous.
Problems pointed out in the foregoing are not intended to be exhaustive but rather are among many that tend to impair the effectiveness of previously known connection techniques. Other noteworthy problems may exist however, those presented above should be sufficient to demonstrate that previous techniques appearing in the art have not been altogether satisfactory, particularly in providing a method and apparatus for quickly and inexpensively connecting one or more lines despite some degree of angular misalignment and without using a seal for alignment functions.